The demand for high capacity rechargeable batteries is strong and growing stronger each year. Many applications, such as aerospace, medical devices, portable electronics, and automotive applications, require high gravimetric and/or volumetric capacity cells. Lithium ion electrode technology provided some improvements in this area. However, to date, lithium ion cells are mainly fabricated with graphite, which has a theoretical capacity of only 372 mAh/g.
Silicon, germanium, tin, and many other materials are attractive active materials because of their high electrochemical capacity. For example, silicon has a theoretical capacity of about 4200 mAh/g, which corresponds to the Li4.4Si phase. Yet, many of these materials are not widely used in commercial lithium ion batteries. One reason is that some of these materials exhibit substantial changes in volume during cycling. For example, silicon swells by as much as 400% when charged to its theoretical capacity. Volume changes of this magnitude can cause substantial stresses in the active material structures, resulting in fractures and pulverization, loss of electrical and mechanical connections within the electrode, and capacity fading.
Conventional electrodes include polymer binders that are used to hold active materials on the substrate. Most polymer binders are not sufficiently elastic to accommodate the large swelling of some high capacity materials. As a result, active material particles tend to separate from each other and the current collector. Overall, there is a need for improved applications of high capacity active materials in battery electrodes that minimize the drawbacks described above.